title: Mass spectrometric studies shed light on unusual oxidative transformations of 1,2-dehydro-N-acetyldopa.
abstract: BACKGROUND
  Lamellarins are a group of over 70 plus bioactive marine natural compounds possessing a 6,7-dihydroxycoumarin moiety. Although they appear to derive from 3,4-dihydroxyphenylalanine (dopa), practically nothing is known about the metabolic fate of these compounds. Biochemical considerations indicate that they could arise from a N-acetyl-1,2-dehydrodopa precursor through oxidative cyclization reaction.
  
  
  METHODS
  To assess the above hypothesis, we synthesized N-acetyl-1,2-dehydrodopa and conducted oxidation studies with commercially available mushroom tyrosinase and evaluated the course of the reaction with reversed-phase liquid chromatography/mass spectrometry (LC/MS).
  
  
  RESULTS
  Mushroom tyrosinase readily oxidized N-acetyl-1,2-dehydrodopa - not to the normally expected quinone - but to an unstable quinone methide isomer, which rapidly cyclized to produce the dihydroxycoumarin product, 3-aminoacetyl esculetin. Interestingly, 3-aminoacetyl esculetin was further oxidized to a second quinone methide derivative that exhibited an addition reaction with the parent dihydroxycoumarin generating dimeric and other oligomeric products in the reaction mixture.
  
  
  CONCLUSIONS
  LC/MS analysis of the N-acetyl-1,2-dehydrodopa oxidation reaction reveals not only a possible novel oxidative cyclization route for the biosynthesis of coumarin-type dehydrodopa compounds in marine organisms, but also unusual oxidative transformations of dehydro dopa derivatives.
authors.affiliation: Department of Biology, University of Massachusetts Boston, Boston, MA 02125, USA.
authors.forename: Adal
authors.initials: A
authors.lastname: Abebe
authors.forename: Qun F
authors.initials: QF
authors.lastname: Kuang
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Evans
authors.forename: Manickam
authors.initials: M
authors.lastname: Sugumaran
mesh_terms: D000363:Agaricales / Q000201:enzymology; D055162:Biocatalysis; D001711:Biotransformation; D005656:Fungal Proteins / Q000737:chemistry*; D007980:Levodopa / Q000031:analogs & derivatives* / Q000737:chemistry; D013058:Mass Spectrometry; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D005656:Fungal Proteins; D007980:Levodopa; D014442:Monophenol Monooxygenase